Viral infections caused by Herpes Simplex virus-1 (HSV-1), often occur as a result of a compromised immune system. The innate immune system is the first line of defense against prevention of these pathogens and consists of numerous soluble factors and cell types, including dendritic cells (DC) and natural killer cells. One type of DC, the plasmacytoid DC (PDC) is important in innate immune function through the production of interferon-? (IFN) induced by enveloped viruses like HSV-1. PDC have recently been shown to play a role in induction of Th1 immunity against influenza and HSV-1 and are recruited in mouse infection models to lymph nodes to stimulate antiviral cytotoxic T-cells. In AIDS patients, the lack of PDC in the circulation, along with depletion of CD4 T-lymphocytes is associated with the development of opportunistic infections, including viral infections. In addition to IFN, PDC produce chemokines and tumor necrosis factor-a upon HSV stimulation. We demonstrated that PDC also produce human beta-defensin-1 (hBD-1), an antimicrobial peptide that has antiviral activity and chemotactic properties towards cells transfected with CCR6 receptor. We hypothesize that an initial step in anti-viral immunity against HSV-1 is the production of hBD-1 in immune cells such as PDC. Our preliminary data show that HSV-1 induces increased hBD-1 mRNA and peptide in PDC within 2 hours of HSV-1 stimulation. Since PDC have potential importance in viral infections, it is essential to first understand the nature and mechanism of the viral induction of hBD-1 in PDC before determining its presence in clinical disease in patients. We hypothesize that HSV-1 directly induces relevant amounts of hBD-1 in PDC via stimulation of Toll-like receptor 9 and activation of transcription factors subsequently increasing hBD-1 gene transcription. This study proposes to explore the initial response pathway of HSV-1 induced hBD-1 mRNA and peptide in PDC, to develop a method to quantify hBD-1 induction in this rare DC subset, and to determine the transcriptional activation pathway of hBD-1 induction by HSV-1. In the first aim we will determine whether hBD-1 is stimulated by HSV-1 via a direct pathway or whether cytokines and chemokines influence the induction via an indirect mechanism. We will also study HSV-1 and PDC interactions using co- localization studies of virus and hBD-1 and whether hBD-1 requires endosomal acidification upon viral entry using chloroquine treatment of PBMC. To begin to address the biological function of hBD-1, chemotaxis studies will be done. We will examine TLR 2, 7 and 9 signaling, induction of interferon regulatory factors and identification of binding sites of transcription factors in the hBD-1 promoter region. The data from this grant will yield new information on a new mechanism for [unreadable]-defensin regulation, different from hBD-2, and enhance the knowledge of the biological function of PDC and also enable future studies in vivo, designing animal studies that model HSV-1 infection or clinical studies. Herpes Simplex Virus-1 (HSV-1) is the cause of severe and often persistent opportunistic infections in immunocompromised patients, such as those undergoing chemotherapy, organ transplantation, and those with immunodeficiencies and HIV. The first line of defense against this and other viral pathogens is the innate immune system. One component of innate immunity is the production of antibiotic peptides such as [unreadable]- defensins. The long-range goal of our research is to understand the role of [unreadable]-defensins in the innate immune defense against viruses so that novel therapies can be developed from our findings.